Hydraulic draft gear and cushioning unit

ABSTRACT

A double-acting hydraulic cushion unit for a railway car which is formed with a hydraulic-fluid-filled cylinder having a closed end and an open end afforded by an apertured cylinder head. A piston assembly is disposed for relative reciprocating movement within the cylinder and includes a piston rod which slidingly moves through the cylinder head. The unit is provided with a flexible accumulator boot connected to the cylinder head and to the piston rod to close the open end of the cylinder. A metering means comprises a metering pin on the cylinder which cooperates with a slidable orifice plate in the piston, the orifice plate having one position in buff impact and another position on the return stroke of the piston assembly to facilitate the transfer of fluid from one side of the piston head to the other. A fluidpressure-responsive valve means is movably disposed in a chamber contiguous with the accumulator to a position overlying passages communicating with the accumulator and to a position clear of said passages. The fluid-pressure-responsive valve is designed to also restrict the flow of fluid from one side of the piston during the return stroke of the piston and upon a draft impact stroke to cushion said impact. The piston rod also includes metering openings also serving on the return stroke to meter the fluid to the accumulator boot. In one embodiment relief valves are provided in the piston to open upon predetermined fluid pressures on opposite sides of said piston.

United States Patent [72] Inventor William H. Peterson llomewoodJll.[21] AppLNo. 799,175 [22] Filed Feb. 14,1969 [45] Patented Ang.3, 1971[73] A'ssignee Pullman-Incorporated ChicagoJll.

[54] HYDRAULIC DRAFT GEAR AND CUSHIONING UNIT 14 Claims, 12 DrawingFigs.

[52] US. 213/8, 213/43. 188/88, 267/115 [51] Int. B6lg9/04, B6lg9/12[50] FleldolSeareh 213/8,43, 223; 267/115; 188/88.509, 88.510, 96,100

56 immense UNITED STATES PATENTS 3,070,363 12/1962 Ellis,.lr 213/433,190,458 6/1965 Zanow... 213/43 3,232,443 2/1966 Smith 213/8 $275,164911966 Peterson 213/43 3,412,870 11/1968 Rollins..... 213/8 3,458,0547/1969 Thompson 213/43 Primary ExaminerDrayton E. HoffmanAttorneys-Hilmond O. Vogel and Wayne Morris Russell ABSTRACT: Adouble-acting hydraulic cushion unit for a railway car which is formedwith a hydraulic-fluid-filled cylinder having a closed end and an openend afforded by an apertured cylinder head. A piston assembly isdisposed for relative reciprocating movement within the cylinder andincludes a piston rod which slidingly moves through the cylinder head.The unit is provided with a flexible accumulator boot connected to thecylinder head and to the piston rod to close the open end of thecylinder. A metering means comprises a metering pin on the cylinderwhich cooperates with a slidable orifice plate in the piston, theorifice plate having one position in buff impact and another position onthe return stroke of the piston assembly to facilitate the transferof-fluid from one side of the piston head to the other. Afluid-pressure-responsive valve means is movably disposed in a chambercontiguous with the accumulator to a position overlying passagescommunicating with the accumulator and to a position clear of saidpassages.- The fluid-pressure-responsive valve is designed to alsorestrict the flow of fluid from one side of the piston during the returnstroke of the piston and upon a draft impact stroke to cushion saidimpact. The piston rod also includes metering openings also serving onthe return stroke to meter the fluid to the accumulator boot. In oneembodiment relief valves are provided in the piston to open uponpredetermined fluid pressures on opposite sides of said piston.

PATENTEDAUS 3911 3596173 sum 1 or 5 IN VE N TOR L WILLIAM H. PETERSON 8%ATT'Y.

PATENTEDAUB 3197a v SHEET 2 or 5 W W: a z

. I u i .1 Lg] INVENTOR WILLIAM H. PETERSON Mai/723 PATENTEDAUB 3m:

sum 3 or s INVENTOR WILLIAM H. PETER N BY Wa KTT'Y.

PATENTEU Aus 3:911

SHEET Q [If 5 INVENTOR WILLIAM H. PE ERSON PATENTEUAUB 3m 3596.773

' sum 5 [IF 5 INVENTOR p I l lll WILLIAM H. PETERSON WfiM AT'T'Y.

nvmuuuc mum'r GEAR AND cusmoumc uurr SUMMARY unit particularly adaptedfor railroad cars which during operation provides cushioning for bothbuff and'draft impacts to which a railroad car is subjected. Thecushioning unit of the present invention may readily be incorporated inthe underframe' at opposite ends of the car to provide end-of-carcushioning for the impacts which are applied to the coupler of the car.A primary object of the present invention is to provide a cushioningunit having a metering pin arrangement which cooperates with a meteringorifice provided in the piston head of the unit. The meteringarrangement provides for a substantially constant force travel of thepiston relative to the cushioning cylinder in a buff impact condition.Further, the metering arrangement includes a sliding orifice plate whichduring return of the piston to a neutral position is movable to DETAILEDDESCRIPTION Referring now particularly to FIGS. 1 through 4 and 7, ahydraulic cushion unit is designated by the reference character 10. Thehydraulic cushion unit 10, as shown in FIG. The invention relates to ahydraulic draft gear or cushioning provide an increased flow of fluid toa chamber containing the metering Jpin thus assuring the quick return ofthe unit to its neutral position. Further, the piston assembly isdisposed in the neutral position in lengthwise spaced relation from acylinder head forming one end of the cylinder thus permitting a limitedtravel of the piston towards said cylinder head in the event of theapplication of a draft'impact. The cylinder head is provided with acavity and a slidable valve assembly which in a buff position permitsfluid flow from a flexible accumulator to a chamber disposed between thecylinder head and one side of the piston. The valve assembly is sodisposed relative to the cylinder rod of the piston assembly as topermita restricted flow of the fluid to said accumulator from saidlast-mentioned chamber during the return stroke and during a draftimpact thereby providing cushioning or snubbing to absorb the forces ofthe said-draft impact. In amodified embodiment thepiston rodis furtherprovided with metering openings which also during the-return stroke ofthe piston head provide'for a smooth retumof the unit to a neutralposition. The piston'assembly has a piston rod which is connected toa-yolte arrangement asv sociated with a standard coupler. The yokearrangement provides' with a center still a pair of pockets disposed onopposite sides of the yoke which contain leaf springs adapted to returnthe piston assembly to its neutral position aftera draft impact.

BRIEF DESCRIPTION OF THE DRAWINGS FIGQI is a schematic plan view of oneend of a railroad car showing an underframe having at one end thereof ahydraulic draft gear and cushion unit;

FIG. 2 isa plan view partially in section of -an end-of-car cushion unitin one end of a car underframe;

FIG. 3 is a side elevational view of the arrangement shown in FIG. 2;

FIG. 4 is a cross-sectional'view through a hydraulic cushion unitdisposed in the center sill of a railroad car underframe;

FIG. 5 is a cross-sectional view showing the connection of a coupler toa yoke, connected to the piston rod of a piston assembly;

FIG. 6 is a cross sectional view similar to FIG. 4 disclosing a modifiedhydraulic cushion unit;

FIG. 7 is a perspective view of a modification of the cushioning unitdisclosed in FIG. 4;

FIG. 8 is a frontal elevational view of a piston assembly;

FIG. 9 is a cross-sectional view taken substantially along the line 9-8of FIG. 8;

FIG. 10 is a cross-sectional view taken substantially along the line10-10 of FIG. 9;

FIG. 11 is a cross-sectional view taken substantially along the line11-11 of FIG. 9; and

FIG. 12 is a detail cross-sectional view of a relief valve.

1, is positioned at the ends of a railroad car 11 having a conventionalunderframe 12 including a center sill 13. The hydraulic unit 10 includesa cylinder 14 having a closed end formed by an end plate 15. The endplate 15 has connected thereto a metering pin 16 disposed in a chamberA. The metering pin 16 includes tapering metering slots 17. A cylinderhead 18 is disposed intermediate the ends of the cylinder 14 and isdisposed therein within an annular undercut 19. An annular valve plate20 is also disposed in the undercut 19 and includes ports 21 whichcommunicate with a chamber B as best shown in FIG. 7. A suitable lockingarrangement 22 locks the valve plate 20 and cylinder head 18 in theundercut 19. A valve element or ring 23 is longitudinally movable withinan annular recess or chamber 24 provided in the cylinder head 18. Asimilar valving arrangement is shown in applicant's US. Pat. No. Re.26,472, issued Oct. 1, I968.

A piston assembly is generally designated at 25 and includes a rod 26having an elongated bore 27. A piston 28 connected to the rod 26 has afrontal side which with the end plate 15 forms the chamber A and withits rear side, the annular valve plate 20' and cylinder head 18 formsthe chamber B. The piston 28 is provided with a laminated plastic slidering 29 suitably described in the aforementioned patent. The piston 28as indicated at 30 is threaded to the end of the rod 26 and in itsfrontal face is provided with an enlarged annular bore 31 in which asnap ring 32 is secured. A metering plate 33 is longitudinally slidablycontained within the bore 31 and includes an arcuate peripherallyextending edge 34. A plurality of circumferentially extending bores 35are provided in the metering plate 33 about a longitudinally extendingmetering orifice 36.

The piston 28 is provided with a pair of vertically spacedlongitudinally extending bores 37 and a pair of transversely spacedlongitudinally extending bores 28.'Relief valves 39 and 40, as bestshownin FIGS. 8 and 9, are respectively provided in the bores 37 and 38.Relief valves 39 and 40 have certain common parts each including tubularspool-shaped body 41 having an end 42 and an annular undercut passagev43. The end 42 includes bleed openings 44 and a substantially smalltubular piston element 45, which is adapted to be slidingly engagedwithin a bore 46 provided in the piston 28. 1

As best shown in FIGS. 4 and 9, the relief valves 39hav theirpistonelements facing the chamber B and these are effective to operate duringcertain excessive draft impacts. The relief valves 40 have their pistonelements 45 facing the chamber A and are effective during certainexcessive buff impacts. The relief valves 39 include retainer elements47 having projections 48 provided with open end bores 49. The retainerelements 47 are retained within the bores 37 by means of snap rings 50.Springs 51 within the bodies 41 bias the piston elements 45 in theposition indicated in FIG. 9. As best shown in FIG. 12, one of therelief valves 40 is disclosed and the spring 51 is wrapped about aretainer element 47' having an open end bore 48 and being suitablythreaded into the piston 28. The piston element 45 of each relief valve40 is movable within a bore 53 provided in an annular retaining plate 52suitably secured relative to the bore 37 by means of a snap ring As bestshown in FIGS. 7, 9 and 12, the piston 28 is provided with annularpassages 54 and 55 encircling the relief valves 39 and 40. An annularpassage 56 is also provided in one end of the piston rod 26 whichcommunicates with openings 57 opening inwardly with respect to theelongated bore 27 The annular passage 56 communicates with the annularpassages 54. As best shown in FIGS. 7 and 8 the frontal face of thepiston 28 is provided with a plurality of passages 58 which open intothe chamber A. The passages 58 are in direct communication with theannular passages 55 of the piston 28. The rear face of the piston 28 asshown in FIG. 11 is also provided with similar-passages 59 opening intothe chamber B and being in communication with the annular passages 54.

The cylinder 14 is closed by a flexible accumulator boot 60 having oneend sealingly connected to the piston rod 26 by means of a connectingarrangement 61 more specifically described in the aforementioned patent.The accumulator boot 60 includes an open end portion 62 which is alsosealingly connected to the intermediate cylinder head 18 by means of asecuring ring 63. The bore 27 by means of a plurality of openings 64 isin communication with the interior of the accumulator boot 60.Theintermediate cylinder head 18 includes a bore 65 which encircles thepiston rod 26 and is circumferentially spaced with respect thereto. Thebore 65 communicates with an enlarged annular bore 66 provided in thevalve plate 20 and which also is circumferentially spaced relative tothe piston rod 26.

The ports 21, the annular chamber or recess 24, and bores 65 and 66,provide a passageway means from the chamber B to the accumulator boot60. The bore 27 with the openings 64 and 100 leading to the accumulatorboot 60 provide a passageway system in the piston rod 26, communicatingthe chamber A with the accumulator boot 60.

Referring now particularly to FIGS. 2and 3, the center sill 13.0ftheunderframe 12 includesa pair of upright walls 70 having at their lowerends outwardly projecting flanges 71 and having a top wall 72. Atransversely extending stop 73 is supported on the walls 70 withinthe'center sill-13, and provides a pocket 74 in which the cushion unit'10 is disposed. The end plate 15 of the cylinder 14 is provided with,forwardly projecting stop elements 75 which are longitudinally slightlyspaced from from stop lugs 76 extending through openings 77 in thevertical walls 70. The lugs 76 are retained in position by means ofbrackets 78 suitably connected to the upright walls 70. Thus thecylinder 14 is restrained against limited longitudinal movement withinthe center sill by the stop 73 and the top ele- -rnents 75'and 76.

As best shown in FIGS. 4 and 6, a spring retainer plate 79 is fixed onthe cylinder 14 and supports one end of a spring 80 encircling a portionof the cylinder 14 and the piston assembly, said spring 80 being inengagement with the rear wall portion 81 of a yoke 82. The yoke 82 isprovided with laterally projecting vertical lug elements 83 which withthe vertical walls 70 and inwardly projecting stop lugs 84 provide aleaf spring pocket 85 on each side of the yoke 82. Lugs project throughopenings 86 in the walls 70 and are secured by means of brackets 87-tothe upright walls 70: A' pair of leaf spring assemblies 88 are disposedin each of the pockets 85 in the manner indicated in FIG. 2..The ends ofthe center sill 13 are also provided with a bottom cover plate 89.

As best shown in FIG. the yoke 82 is provided with a spherical socket 91and a bore 92 into which the piston rod 26 projects. A threadedconnecting member 93 conforming to the spherical socket 91 is suitablythreaded on the end of the rod 26. The connector 93 has an arcuatecoupler-engaging surface 94 which is adapted to receive the arcuate endof a coupler stem 95. The stem 95 is provided at its forward end with aconventional coupler head 96. The yoke 82 is also provided at itsforward end with a suitable bell-mouth structure 97- of conventionaldesign. The stem 95 is mounted for relative pivotal and sliding movementby means of a key 98 which is carried on the coupler stem 95 and slideswithin elongated slots 99 of the yoke 82.

THE OPERATION The chambers A and B, passageway means, and passageway Isystem are completely charged with a suitable hydraulic fluid.

passes through the metering orifice 36 providing a constant force travelof the piston 25. The fluid passing from the chamber A through the bore27 passes into the accumulator 60. The pressure differential between theaccumulator 60 and the chamber B provides for movement of the valveelement 23 into engagement with the valve plate 20 uncovering the bore65 thereby freely permitting fluid from the accumulator 60 to fill upthe chamber B. During the buff impact, the orifice plate 33 is anengagement with the end of the piston rod 26 whereupon the bores 35 arecovered. 7

Upon cessation of the buff force the spring'80 returns the pistonassembly 25 to the neutral position shown in FIG. 4. Upon such returnmovement the orifice plate 33 moves into engagement with the snap ring32 and the bores 35 are now incommunication with the bore 27 permittinga volume flow into thechamber A, thus, assuring the quick return of thepiston 28 to its neutral position. During this return movement of thepiston 28 the valve element 23 is disposed over the bore 65 so a limitedor restricted flow of fluid is possible since, as best shown in FIG. 7,The inner peripheral surface of the valve element 23 is of arcuateconstruction providing with the piston rod 26 a small annular passage 23through which a restricted flow of fluid can pass from the chamber Bonto the accumulator 60 'as best shown in FIG. 7. The restrictedpassage23 provides for the smooth andeven return of the piston'head 28 to theneutral position. The valve'element 23 thus moves to its open positionon the buff or closing stroke'of the piston 28. On the return stroke ofthe piston 28 toits neutral position the valve element 23 is in apartially closed position over the bore 65 through permitting by virtueof the opening 23' a restricted flow of fluid to the accumulator 60.

In the embodiment shown in FIG. 7, the piston rod 26 is also providedwith metering openings 100 communicating with the bore 27 and theaccumulator boot- 60. During the return stroke these openings alsofunction as metering openings to return fluid from the chamber B to theaccumulator boot 60 in a smooth and efficient manner. If desired, theopening 23' may be substantially eliminated by providing a tightersliding fit with the piston rod 26 in which'case the metering on thereturn stroke is provided solelyby the metering openings 100.

In the event of a draft impact on the coupler head 96, the yoke 82 movesin a direction away from the cylinder 14 compressing the leaf springassemblies 88 until they are in flat contiguous relation which thenprevents further outward movement of the yoke 82. Simultaneously, thepiston28 is moved toward the valve plate 20 and fluid from the chamber8- flows through the ports 21, bore 66, through the restricted opening23' into the accumulator boot 60. The restriction provided by theopening 23' results in a cushioning or snubbing actionfor cushioning thedraft impact during its application. During such draft impact fluid fromthe bore 27 is free to pass through the'metering orifice 36 and throughthe bores 35. Upon the cessation of the draft impact the leaf springassemblies 88 return the piston 28 to the neutral position shown in FIG.4. Thus it can be seen that the metering pin 16 with the meteringorifice 36 provides a constant force travel of the piston 28 during thebuff stroke. On the draft impact stroke the valve element 23 provides asufficient restriction of fluid flow from the chamber B into theaccumulator 60 to afford the cushioning or snubbing action during saidimpact.

In FIG. 6 a further modified cushion unit 10 is disclosed. The primarydifference between the cushion unit of FIG. 6 and that shown in theother FIGURE is that the relief valves 39 and 40 are absent from thepiston head 28. Otherwise all of the parts are the same and are sodesignated. In certain applications and constructions it may bedesirable to eliminate-the relief valves. In operation the relief valvesfunction as follows: during a buff stroke of the piston 28, provided thepressure within chamber A exceeds a predetermined amount, the pistonelements 45 of the relief valves 40 will move causing the annularundercut passage 43 of each relief valve body 41 to provide forcommunication between the annular passages 54 and 55. Fluid thus can nowflow through the openings 58 through the annular passages 54 and 55 tothe annular passage 56 and through openings 57 into the interior of thebore 27 which fluid ,is then directed through the openings 64 to theaccumulator boot 60. I

In the'event that the fluid pressure within the chamber B exceeds apredetermined amount the piston elements 45 facing the chamber 8 aremoved to open the valves 39 wherein the undercut passage 43 provides forcommunication between the annular passages 54 and 55. Fluid may now flowthrough the openings 59, as best shown in H6. 11, through the passages54 and into passages 55 which permit fluid to flow through the openings58 into the chamber A, thus relieving the excessive pressures of chamber8. The bleed openings 44 and 49 of the relief valves 40 are provided topermit free operating movement of therelief valves since the unit iscompletely filled with hydraulic fluid.

As previously described, a limiting tilting movement of the cylinderfrom the horizontal is permitted by the loose clearance provided by thestop elements 75 relative to the lugs 76. The yoke 82 is not confinedfor guiding movement within the sill l3 and thus during buff impact allforces to be dissipated are absorbed first in the hydraulic cushioningdevice. Precise guiding of the yoke 82 is not required since theflexible boot does not require the precision of guiding movementrequired in cushioning devices having sliding SCQISpThUS the totalforces are first absorbed in the cushioning device.

What 1 claim is:

l. A double-acting hydraulic cushion unit for relieving the buff anddraft impacts imposed on the couplers of a railway car, said cushionunit comprising:

a cylinder having a closed end and an open end,

a piston assembly including a piston head and a piston rod disposed insaid cylinder having lengthwise travel relative to said closed end,

a cylinder head mounted in said cylinder adjacent said open end andhaving passageway means, said piston rod being movable through saidcylinder head during said travel,

a flexible accumulator connected between said cylinder and said pistonrod for closing the open end of said cylinder, said passageway meansproviding communication between a first chamber defined by said pistonhead and said cylinder head,

valve means disposed in said passageway means and operable upon apredetermined pressure differential between said first chamber and asecond chamber defined by said piston head and said closed end toprovide fluid flow from said accumulator through said passageway meansto said first chamber,

said valve means having restrictive flow means being operable during themovement of said piston assembly in a draft direction toward saidcylinder head for permitting a restricted flow of fluid from said firstchamber to said accumulator;

a passageway system formed in said piston rod providing communicationbetween said second chamber and said accumulator,

hydraulic fluid filling said chambers and means metering the flow ofsaid fluid between the second and first chambers during travel of saidpiston head,

said metering means including a metering pin having a me tering surfaceand being supported by said cylinder within said second chamber,

said piston having a bore facing said second chamber and communicatingwith said passageway system,

a metering element disposed in said bore and having limited axialmovement relative to said piston, said metering element including ametering orifice cooperating with said metering orifice cooperating withsaid metering surface during lengthwise travel of said piston assemblytoward said closed end to meter the flow of fluid from said secondchamber to said passageway system,

said metering element having at least one opening radially spacedrelative to said orifice which during the aforesaid travel of saidpiston assembly is in a position closed by said piston'assembly andwhich during movement of said piston assembly in an opposite directionis axially moved within said bore, and said opening of said meteringelement communicates with said passageway system and said secondchamber.

2. The invention in accordance with claim 1,

wherein said metering element includes aplurality of said radiallydisposed and circumferentially disposed openings which during traveltoward said closed end are closed by an adjacent wall portion of saidpiston assembly and which during travel in an opposite direction aremoved from said wall portion permitting fluid flow therethrough.

3. The invention in accordance with claim 1 said valve means comprisinga port in said passageway means providing communication between saidfirst chamber and said accumulator, and

a valve element shiftable during a pressure differential between saidfirst chamber and said accumulator to positions opening said port andpartially blocking said port.

4. The invention in accordance with claim 3,

said valve element comprising a ring-shaped valve plate encircling saidpiston rod and slidably supported thereon,

and

said valve plate in the partially blocking position of said portproviding for a restricted flow through said passageway means to saidaccumulator.

5. The invention in accordance with claim 1, including:

' relief valve means in said piston head including relief ports openingoutwardly into said first and second chambers,

valve elements in said head adapted to open said ports in response to apredetermined pressure differential between said chambers whereby fluidfrom one chamber is delivered to the other.

6. The invention in accordance with claim 5,

said piston head having a passage providing communication between saidports and said passageway system.

7. In a railway car having an underframe, a double-acting hydrauliccushion unit for relieving the buff and draft impacts imposed on thecouplers of said car, said cushion unit comprising:

a cylinder having a closed end and an open end,

a piston assembly including a piston head and a piston rod disposed insaid cylinder having lengthwise travel relative to said closed end,

a cylinder head mounted in said cylinder adjacent said open end andhaving passageway means including at least one opening providing formovement of said piston rod during said travel,

a flexible accumulator connected between said cylinder and said pistonrod for closing the open end of said cylinder, said passageway meansproviding communication between a first chamber defined by said pistonhead and said cylinder head,

a second chamber defined by said piston head and said closed end,

a passageway system formed in said piston rod providing communicationbetween said first chamber and said accumulator,

hydraulic fluid filling said chambers and means metering the flow ofsaid fluid between the first and second chambers during travel of saidpiston head; the improvement comprising means connecting said cylinderto said underframe,

a coupler-carrying member connected to said piston rod for traveltherewith,

biasing means between said cylinder and said coupler-carrying memberurging said piston assembly in a direction toward said open end,

first stop means on said underframe,

second stop means on said coupler-carrying member,

said stop means being longitudinally spaced and providing on oppositesides of said coupler-carrying member with said underframe a pluralityof pockets,

spring means disposed in said pockets between said stop means, and in anonoperating position of said piston assembly positioning said pistonhead in relatively spaced relation between said closed end and saidcylinder head, and

valve means on said cylinder head providing with said passageway means arestricted flow of fluid from said first chamber to said accumulatorduring movement of said piston assembly toward said open end during adraft impact whereby said spring means is compressed.

8.. The invention in accordance with claim 7,

said valve means comprising a ring-shaped valve element encircling saidpiston rod and during said movement on a draft impact being adapted topartially block the flow of fluid to said passageway means and to saidaccumulator.

9. The invention in accordance with claim 8,

said spring means comprising a plurality of nested springs.

10. In a railroad car having a center sill structure, a hydrauliccushioning unit for relieving the buff and draft impacts imposed uponthe couplers of said car, said cushioning unit being positioned adjacentand within one end of said center sill structure, and comprising:

a cylinder member having an inner end part and an outer end part facingoutwardly of the car and a piston member including a piston head and apiston rod disposed in said cylinder member and having lengthwise travelrelative to said end parts,

said piston rod extending longitudinally of said sill structure andoutwardly of said outer end part,

metering means for metering hydraulic fluid flow within said cylindermember on buff and draft impacts being applied to said cushioning unitto cushion the application of such impacts to said sill structure,

a coupler-carrying element mounted in said sill structure,

a coupler-carrying element mounted in said sill structure outwardly ofsaid cushioning unit for movement longitudinally of said sill structureand being connected with said piston rod for travel therewith,

means for operatively connecting the car coupler to saidcoupler-carrying element, v

biasing means between said cylinder member and said coupler-carryingelement urging said piston member in a direction toward said outer endpart,

attachment means for securing said cushioning unit to said sillstructure against buff and draft impacts applied to said cushioning unitincluding a resilient cushioning means being disposed within the centersill structure and in general longitudinal alignment with said'biasingmeans interposed between one of said cushioning unit members and saidsill structure for absorbing draft impacts when said piston head isadjacent said outer end part, and stop means being carried within saidsill structure and said 7 coupler-carrying element for limiting movementof one of said cushioning unit members in draft,

said stop means including a first stop on said center sill structure anda second stop cooperative with one of said cushioning unit members, saidsecond stop being longitudinally spaced from said first stop and saidresilient cushioning means being disposed between said stops.

11. The invention according to claim 10, and

said second stop being carried by said coupler carrying element.

12. The invention according to claim 10, and

said resilient cushioning means including spring means disposed betweensaid first and second stops.

13. The invention according to claim 10, and

said resilient cushioning means including a plurality of nested springs.

14. The invention according to claim 10, and

a flexible expansible boot being connected between said cylinder memberand said piston rod to provide a seal between said cylinder member andsaid piston rod.

1. A double-acting hydraulic cushion unit for relieving the buff anddraft impacts imposed on the couplers of a railway car, said cushionunit comprising: a cylinder having a closed end and an open end, apiston assembly including a piston head and a piston rod disposed insaid cylinder having lengthwise travel relative to said closed end, acylinder head mounted in said cylinder adjacent said open end and havingpassageway means, said piston rod being movable through said cylinderhead during said travel, a flexible accumulator connected between saidcylinder and said piston rod for closing the open end of said cylinder,said passageway means providing communication between a first chamberdefined by said piston head and said cylinder head, valve means disposedin said passageway means and operable upon a predetermined pressuredifferential between said first chamber and a second chamber defined bysaid piston head and said closed end to provide fluid flow from saidaccumulator through said passageway means to said first chamber, saidvalve means having restrictive flow means being operable during themovement of said piston assembly in a draft direction toward saidcylinder head for permitting a restricted flow of fluid from said firstchamber to said accumulator; a passageway system formed in said pistonrod providing communication between said second chamber and saidaccumulator, hydraulic fluid filling said chambers and means meteringthe flow of said fluid between the second and first chambers duringtravel of said piston head, said metering means including a metering pinhaving a metering surface and being supported by said cylinder withinsaid second chamber, said piston having a bore facing said secondchamber and communicating with said passageway system, a meteringelement disposed in said bore and having limited axial movement relativeto said piston, said metering element including a metering orificecooperating with said metering orifice cooperating with said meteringsurface during lengthwise travel of said piston assembly toward saidclosed end to meter the flow of fluid from said second chamber to saidpassageway system, said metering element having at least one openingradially spaced relative to said orifice which during the aforesaidtravel of said piston assembly is in a position closed by said pistonassembly and which during movement of said piston assembly in anopposite direction is axially moved within said bore, and said openingof said metering element communicates with said passageway system andsaid second chamber.
 2. The invention in accordance with claim 1,wherein said metering element includes a plurality of said radiallydisposed and circumferentially disposed openings which during traveltoward said closed end are closed by an adjacent wall portion of saidpiston assembly and which during travel in an opposite direction aremoved from said wall portion permitting fluid flow therethrough.
 3. Theinvention in accordance with claim 1, said valve means comprising a portin said passageway means providing communication between said firstchamber and said accumulator, and a valve element shiftable during apressure differential between said first chamber and said accumulator topositions opening said port and partially blocking said port.
 4. Theinvention in accordance with claim 3, said valve element comprising aring-shaped valve plate encircling said piston rod and slidablysupported thereon, and said valve plate in the partially blockingposition of said port providing for a restricted flow through saidpassageway means to said accumulator.
 5. The invention in accordanCewith claim 1, including: relief valve means in said piston headincluding relief ports opening outwardly into said first and secondchambers, valve elements in said head adapted to open said ports inresponse to a predetermined pressure differential between said chamberswhereby fluid from one chamber is delivered to the other.
 6. Theinvention in accordance with claim 5, said piston head having a passageproviding communication between said ports and said passageway system.7. In a railway car having an underframe, a double-acting hydrauliccushion unit for relieving the buff and draft impacts imposed on thecouplers of said car, said cushion unit comprising: a cylinder having aclosed end and an open end, a piston assembly including a piston headand a piston rod disposed in said cylinder having lengthwise travelrelative to said closed end, a cylinder head mounted in said cylinderadjacent said open end and having passageway means including at leastone opening providing for movement of said piston rod during saidtravel, a flexible accumulator connected between said cylinder and saidpiston rod for closing the open end of said cylinder, said passagewaymeans providing communication between a first chamber defined by saidpiston head and said cylinder head, a second chamber defined by saidpiston head and said closed end, a passageway system formed in saidpiston rod providing communication between said first chamber and saidaccumulator, hydraulic fluid filling said chambers and means meteringthe flow of said fluid between the first and second chambers duringtravel of said piston head; the improvement comprising means connectingsaid cylinder to said underframe, a coupler-carrying member connected tosaid piston rod for travel therewith, biasing means between saidcylinder and said coupler-carrying member urging said piston assembly ina direction toward said open end, first stop means on said underframe,second stop means on said coupler-carrying member, said stop means beinglongitudinally spaced and providing on opposite sides of saidcoupler-carrying member with said underframe a plurality of pockets,spring means disposed in said pockets between said stop means, and in anonoperating position of said piston assembly positioning said pistonhead in relatively spaced relation between said closed end and saidcylinder head, and valve means on said cylinder head providing with saidpassageway means a restricted flow of fluid from said first chamber tosaid accumulator during movement of said piston assembly toward saidopen end during a draft impact whereby said spring means is compressed.8. The invention in accordance with claim 7, said valve means comprisinga ring-shaped valve element encircling said piston rod and during saidmovement on a draft impact being adapted to partially block the flow offluid to said passageway means and to said accumulator.
 9. The inventionin accordance with claim 8, said spring means comprising a plurality ofnested springs.
 10. In a railroad car having a center sill structure, ahydraulic cushioning unit for relieving the buff and draft impactsimposed upon the couplers of said car, said cushioning unit beingpositioned adjacent and within one end of said center sill structure,and comprising: a cylinder member having an inner end part and an outerend part facing outwardly of the car and a piston member including apiston head and a piston rod disposed in said cylinder member and havinglengthwise travel relative to said end parts, said piston rod extendinglongitudinally of said sill structure and outwardly of said outer endpart, metering means for metering hydraulic fluid flow within saidcylinder member on buff and draft impacts being applied to saidcushioning unit to cushion the application of such impacts to said sillstructure, a coupler-carrying element mounted in said sill sTructure, acoupler-carrying element mounted in said sill structure outwardly ofsaid cushioning unit for movement longitudinally of said sill structureand being connected with said piston rod for travel therewith, means foroperatively connecting the car coupler to said coupler-carrying element,biasing means between said cylinder member and said coupler-carryingelement urging said piston member in a direction toward said outer endpart, attachment means for securing said cushioning unit to said sillstructure against buff and draft impacts applied to said cushioning unitincluding a resilient cushioning means being disposed within the centersill structure and in general longitudinal alignment with said biasingmeans interposed between one of said cushioning unit members and saidsill structure for absorbing draft impacts when said piston head isadjacent said outer end part, and stop means being carried within saidsill structure and said coupler-carrying element for limiting movementof one of said cushioning unit members in draft, said stop meansincluding a first stop on said center sill structure and a second stopcooperative with one of said cushioning unit members, said second stopbeing longitudinally spaced from said first stop and said resilientcushioning means being disposed between said stops.
 11. The inventionaccording to claim 10, and said second stop being carried by saidcoupler carrying element.
 12. The invention according to claim 10, andsaid resilient cushioning means including spring means disposed betweensaid first and second stops.
 13. The invention according to claim 10,and said resilient cushioning means including a plurality of nestedsprings.
 14. The invention according to claim 10, and a flexibleexpansible boot being connected between said cylinder member and saidpiston rod to provide a seal between said cylinder member and saidpiston rod.